1. Field of the Invention
This invention lies in the field of measurement of the blood pressure of living animals and persons. While it uses the same type of cuff and cuff pressure variations as are used in other methods, it utilizes a more reliable method of determining when the oscillations are valid, and when they are not. That is, when there may be artifacts. More particularly, this invention is related to the measurement of systolic, diastolic, and mean arterial pressures involved, in the blood pressure cycle.
2. Description of the Prior Art
As cuff pressure is reduced, less pressure is applied to the underlying artery. The length of time that the artery is occluded is decreased as the cuff pressure is reduced to just below the systolic pressure, the force of the systolic pressure forces the occluded artery open, and blood flows through the artery in spurts, and the amplitudes of the oscillations increase. In the oscillographic method of measuring blood pressure the systolic pressure magnitude of the oscillations induced into the cuff, changes from a steady state to a constantly increasing magnitude. That is, with reduction in cuff pressure, the artery is open for an increasingly larger portion of the heart time cycle and therefore the oscillations increase as the occluding pressure decreases.
With further decrease in cuff pressure, the amplitudes increase up to a maximum value of amplitude of oscillation and the cuff pressure at the time of this maximum amplitude of oscillation is determined as the mean arterial pressure. This is an indirect method of measurement. However, in the industry, it is taken as a valid definition of mean arterial pressure, and has been proved by very precise experimental procedures.
With continued cuff pressure reduction the underlying artery is open throughout the entire cardiac cycle. The arterial wall movement becomes less and less and the amplitude of the cuff pressure oscillation decreases and then becomes uniform and of small amplitude. The point at which the oscillations stop decreasing and become uniform, is noted as the diastolic pressure.
In the prior art, the system which is most often utilized is one in which the cuff pressure is stepped down in value by equal small increments under control of the apparatus. For each value of cuff pressure, as the value of cuff pressure is monitored a comparison of two independent successive measurements of oscillations is performed to determine whether the oscillation measurements are valid. From the amplitude of cuff pressure and the amplitude of oscillation values, one can determine whether the amplitude of oscillation is increasing as the cuff pressure reduces and determine when it reaches a maximum and then starts to reduce, and reduces at a rate which is greater than the rate at which it increased at the start of the measurements.
With the amplitudes of oscillations as recorded at each level of cuff pressure, depending upon a comparison of the two oscillations, it can be determined whether the measurements are valid or, if not, that there are artifacts, or noise, in the blood system, that are hiding the true details of the amplitude of the oscillation.